3. The remote
MCU reports alarms out of order. Specifically, mosaic occurs on the screen, or
the sound is discontinuous.

Handling Process

1. Verify the
fault symptom.

(1) Configure an MP group on the 2 x E1 interface bundling on the NE20.
The remote MCU reports alarms out of order. Specifically, mosaic occurs on the
screen, or the sound is discontinuous.

(2) Ping the link from the local MCU to the NE20. No packets are lost
during the test on 1500-byte packets.

(3) Ping the MP-Group link on the NE20. No packets are lost during the
test on 1500-byte packets, and the delay is normal.

2. Remove 2 x E1 interface bundling and test single E1 links.

(1) Ping the first E1 link on the NE20. No packets are lost during the
test on 1500-byte packets, and the delay is normal.

(2) Ping the second E1 link on the NE20. No packets are lost during the
test on 1500-byte packets, and the delay of the second E1 link is much larger
than that of the first E1 link.

(3) Use the first E1 link on the NE20 to test the MCU. The alarm on the
remote MCU is cleared. No mosaic occurs on the screen. Due to insufficient
bandwidth of the single link, frames are lost occasionally.

(4) Use the second E1 link on the NE20 to test the MCU. The alarm on the
remote MCU is cleared. No mosaic occurs on the screen. Due to insufficient
bandwidth of the single link, frames are lost occasionally.

3. Reproduce the fault after E1 bundling.

4. Analyze the causes of the alarm.

(1) Communicate with the MCU. It is found that the alarm is generated
because the MCU check on the received packets shows that the sequence of packet
sending is inconsistent with that of packet receiving. If too many out-of-order
packets exist, mosaic may occur on the screen and frames may be lost.

(2) Check the NE20 product document. It is found that the MP-Group
interface is deployed in load balancing mode. The sequence of packet sending
and that of packet receiving are inconsistent due to factors such as the link
quality.

Root Cause

1. When the MP-Group interface is bound to multiple links, the physical
features and packet fragment sizes may differ, which causes inconsistency
between the sequence of packet sending and that of packet receiving.

2. The out-of-order IP packets are automatically reassembled based on the
fragment offset field of the IP header. However, if there are strict
requirements for packet sequence and the out-of-order packets are not
effectively reassembled, the MP packet disorder may lead to severe network
performance deterioration and even cause the network to be unavailable.

Solution

1. Perform the
following operations to enable packet order-preserving on the MP-Group
interface:

(1) Enter the MP-Group interface view.

(2) Run the ppp mp reorder command
to enable packet order-preserving function on the MP-Group interface.

(3) Restart the restart command
to restart the MP-Group interface or run the shutdown command and then the undo
shutdown command on the MP-Group interface.

2. Check whether the tested service is normal and the fault is rectified.

Suggestions

1. If the MP-Group interface is bound to multiple links, link delay may
differ due to different link quality. This causes inconsistency between the
sequence of packet sending and that of packet receiving.

2. The out-of-order IP packets are automatically reassembled based on the
fragment offset field of the IP header. However, if there are strict
requirements for packet sequence and the out-of-order packets are not
effectively reassembled, the MP packet disorder may lead to severe network
performance deterioration and even cause the network to be unavailable.

The inconsistency between the sequence of packet sending and that of
packet receiving on the remote MCU causes alarm disorder.